<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>绝对定位练习</title>
    <style>
        div {
            width: 300px;
            background-color: rgba(0, 0, 0, 0.3);
            padding: 10px;
            position: relative; /*做参照物*/
        }

        input {
            width: 260px;
            border: 0px;
            padding: 10px 20px;
        }

        p {
            font-size: 12px;
            color: red;
            margin: 0;
        }

        img {
            position: absolute;
            right: 40px;
            top: 14px;
        }

    </style>
</head>
<body>
<div>
    <input type="text" placeholder="请输入用户名">
    <img src="http://doc.vrd.net.cn/tstore_v1/images/login/yhm.png" alt="">
    <p>用户名不能为空！</p>
</div>

</body>
</html>